The present invention relates to a device and method for controlling movements of a robot.
In operating a manipulator of a robot on the basis of teaching point data, interpolation between the teaching points is usually obtained through the steps described below:
i) determining an interpolation point on the Cartesian space at time intervals;
ii) inversely converting the interpolation point to an interpolation point on the joint space;
iii) according to the interpolation point on the joint space, generating movement data formed of an amount of movement between adjacent interpolation points on the joint space and the time required for movement; and
iv) providing the movement data as instructions to a motor responsible for operating an articulated manipulator of a robot.
However, such articulated robot whose motion is controlled by interpolation cannot always move joint axes at a constant velocity on the joint space, when the tip of the manipulator moves at a constant velocity on the Cartesian space. In particular, movement passing by a singular point can cause a sudden change in velocity of the joint axes. Such abrupt changes in velocity can overload mechanical components including reduction gears forming the joint axes, inviting short mechanical life.
To avoid the problem, it becomes necessary to correct teaching point data so as to lower the velocity of the joint axes to a permissible level. The re-teaching work, however, takes much expense in time and effort of a teaching operator.
As a remedy for the inconvenience, a method introduced in Japanese Patent Application Non-Examined Publication No. H 6-19528 suggests the steps below:
i) obtaining all of movement data for joint axes corresponding to the range between a pair of teaching points;
ii) checking the velocity of the joint axes according to the movement data;
iii) if inadmissible changes in velocity is observed, reducing the velocity of the manipulator""s tip on the Cartesian space, and then a fresh-interpolating the pair of teaching points.
These steps control the change in velocity of the joint axes down to within a permissible value, allowing the tip of the manipulator moves with an automatically controlled velocity. With the method, however, such uniform reduction in velocity between teaching points affects on data having a velocity with no need for slowdown, inviting undesired increase in tact time during operation.
It is therefore the object of the present invention to provide a robot controller capable of driving joint axes at a steady velocity, offering an efficient tact time during operation. According to the present invention, the controller i) stores a series of movement data formed of the amount of movement and the time required for movement; ii) checks whether a movement of a robot has acceleration exceeding a predetermined level according to the stored movement data; iii) increases the time for movement of the corresponding movement data, the preceding data, and the following data, if the movement has acceleration exceeding the permissible level; and iv) controls the robot on the basis of the time-increased movement data. Performing the steps selectively slows down the movement having an acceleration exceeding the permissible level. As a result, undesired change in an acceleration of the joint axes will be lessened, with an increase in the tact time minimized.